JP2002351386A - Plasma display device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To suppress the occurrence of the spurious profile of a moving picture without deteriorating a grey level in the low brightness portion of a PDP(plasma display panel). SOLUTION: One field period of the PDP is divided into subfields SF1 to 6 for a grey level display and subfields SF7 to 12 for continuous light emitting, and the grey level is displayed using the subfields SF1 to 6 when the level value of pixel data is less than 63. When the level value of the pixel data is 63 or more, the gray level is displayed using all subfields SF1 to 6, and at the same time, a subfield for continuous light emitting having a light-emitting period corresponding to the level value obtained by subtracting 63 from the level value of the pixel data is selected to carry out a continuous light emitting display by using this subfield.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a plasma display device, and more particularly, to a plasma display device which suppresses generation of false contours of moving images.

[0002]

2. Description of the Related Art A plasma display panel (PDP) of this type has a plurality of row electrodes arranged for each scanning line, a plurality of column electrodes intersecting the row electrodes, and a row electrode and a column electrode. Discharge cells corresponding to one pixel are formed at the intersections of the electrodes. Since the discharge cell of such a PDP has only two states of light emission and non-light emission, the relative ratio of the display period of one field (one frame period) to the lighting period (sustained light emission period; proportional to the light emission luminance) is each. By dividing the image into a plurality of different subfields, an intermediate gradation display is obtained. Here, when an analog video signal is input, it is converted to image data of a bit number corresponding to the number of subfields by A / D conversion, and a corresponding pixel is converted into an appropriate subfield based on the converted image data. It is lit to represent an intermediate gradation.

[0003] In the example of FIG.
This is an example of displaying 56 gradations, and the most significant gradation bit (8
Bit) corresponds to SF8, and 7
The gray scale bit of the bit is SF7, the gray scale bit of the sixth bit is SF6, the gray scale bit of the fifth bit is SF5,
The fourth gradation bit corresponds to SF4, the third gradation bit corresponds to SF3, the second gradation bit corresponds to SF2, and the lowest gradation bit (first bit) corresponds to SF1. Corresponding. Each subfield SF1 to SF8
Means that the sustained light emission period is, for example, the number of gradations (relative ratio of light emission luminance: proportional to the number of light emission pulses (sustain pulses)) 1, 2,
4, 8, 16, 32, 64, 128 are weighted.

[0004]

As described above, in the PDP device, since the discharge cell of the PDP has only two states of light emission and non-light emission, in order to express an intermediate gray scale, the above-mentioned one is used. The field period is divided into a plurality of subfields, weighting is performed in each subfield in accordance with the luminance level of the pixel data, and the corresponding pixel (that is, the corresponding discharge cell) emits light with the number of times of light emission according to the weighting. I have to. Here, when the sustained light emission period of each subfield is weighted as shown in FIG. 7, when the discharge cell emits light with the number of gradations of 128, light emission is performed only in the subfield SF8 and the number of gradations of 1 is increased.
When light emission is performed in step S27, light emission is performed in subfields SF1 to SF7 other than the subfield SF8. That is, within one field period, the number of gradations is 128.
During the period in which the discharge cells to emit light are emitting light, the discharge cells to emit light at the tone number 127 are in a non-emission state, and during the period when the discharge cells to emit light at the tone number 127 are emitting light. Means that the discharge cells that should emit light at the gradation number 128 are in a non-light emitting state.

Therefore, if a discharge cell to emit light at a tone of 127 and a discharge cell to emit light at a tone of 128 are adjacent to each other, image quality degradation called false contour of a moving image occurs in that area. There is. In order to prevent such image quality deterioration, Japanese Patent Laid-Open No. 2000-231362 proposes a driving method in which a subfield in one field is not inverted from non-light emission to light emission. That is, this driving method is a method in which a pixel to emit light continuously emits light for a period corresponding to the luminance level within one field period. In this driving method, for example, when the number of subfields is 12, 12 gradations can be expressed. However, when 256 gradations such as a television image are required, the shortage of gradations is performed by a method called an error diffusion method. The key is supplemented.

[0006] However, such an error diffusion method,
Since this is a method of expressing one gradation by a plurality of pixels, there is a problem that gradation deterioration is conspicuous in a low luminance portion. Accordingly, an object of the present invention is to suppress the generation of a false contour of a moving image without impairing the deterioration of gradation in a low luminance portion.

[0007]

In order to solve such a problem, the present invention comprises a plurality of row electrodes arranged for each scanning line and a plurality of column electrodes arranged so as to cross the row electrodes. P in which one pixel is formed at the intersection of a row electrode and a column electrode
In a plasma display device for displaying a DP,
A first sub-field group including M sub-fields, each of which has a scanning period and a light-emitting period, each of which has a weighted light-emitting period, and is used for gradation display of pixels; Each pixel is divided into a second subfield group including N subfields each of which has a light emission period and is used for continuous light emission of pixels, and a luminance level value of input pixel data and a preset set value are set. And a light emission control means for controlling the light emission of the pixels by selecting a subfield group according to the determination result of the determination means.

In this case, there is provided subtraction means for subtracting the set value from the luminance level value of the pixel data. When the judgment means judges that the luminance level value of the pixel data is small, the light emission control means determines that the first subfield While selecting a subfield of a light emitting period according to the luminance level value from the group of subfields and performing gradation display of the pixel, when the determining unit determines that the luminance level value of the pixel data is large, the first Of all the sub-fields in the sub-field group is selected to perform the gradation display of the pixels, and the sub-field of the light emission period corresponding to the luminance level value indicating the subtraction result of the subtraction means is selected from the second sub-field group. Is selected so that the pixel emits light continuously. Further, an error diffusion processing unit for performing an error diffusion process when a luminance level value indicating a subtraction result of the subtraction unit is input is provided.
The subfields corresponding to the processing results of the error diffusion processing means are selected from the subfield group of the above (1), and the pixels are made to emit light continuously.

[0009]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below with reference to the drawings. FIG. 2 shows a plasma display panel (PD) constituting the plasma display device according to the present invention.
P) and a block diagram of a drive unit for driving the PDP. The PDP 1 has a plurality of row electrodes X as shown in FIG.
1 to Xm, Y1 to Ym, and a plurality of column electrodes D1 to Dn, which are a plurality of data electrodes, intersecting the row electrodes X1 to Xm, Y1 to Ym. Discharge cells corresponding to one pixel are formed. Also,
The driver 2 that drives the PDP 1 includes a driver 21 that drives the column electrodes D1 to Dn, a driver 22 that drives the row electrodes X1 to Xm, and a driver 2 that drives the row electrodes Y1 to Ym.
And 3.

In such a PDP 1, one field period, which is a display period of one screen, is divided into a plurality of subfields, and gradation display is realized by each subfield. In the present embodiment, as shown in FIG. 3, one field period is divided into twelve subfields SF1 to SF12 to enable display of 256 gradations. Here, each of the subfields SF1 to SF12 is divided into a first subfield group and a second subfield group, and subfields SF1 and SF1 belonging to the first subfield group.
SF2, SF3, SF4, SF5, and SF6 each have a gradation number (that is, a light emission period) of 1: 2: 4: 8: 16: 3.
Weighted as 2. On the other hand, each of the subfields SF7 to SF12 belonging to the second subfield group has the same light emitting period “32”.

FIG. 1 is a block diagram showing a main configuration of a plasma display device according to the present invention. This device is
As shown in FIG. 1, a PDP 1 and a driving unit 2 for driving the PDP 1 perform gradation display of the PDP 1 described above.
And a first light emission control unit 3 for controlling light emission / non-light emission of the pixel in accordance with the bit of the input pixel data a, and determining whether the brightness level of the input image data a and the preset value are large or small. The set value “6” is determined based on the pixel level value comparison unit 4 to be compared and the luminance level value of the input image data a.
3 ”, an error diffusion processing unit 6 that receives the luminance level value of the subtraction result of the arithmetic unit 5 and performs an error diffusion process described later, and a pixel based on the processing result of the error diffusion processing unit 6. And a second light emission control unit 7 for controlling the light emission.

Next, an outline of the operation of the plasma display device configured as described above will be described. When an analog video signal is input, the apparatus performs A / D conversion to 8-bit data, temporarily stores the 8-bit data in a frame memory (not shown), and reads the 8-bit pixel data a from the frame memory based on a synchronization signal. The image data a read from the frame memory is output to the driving unit 2 and output to the column electrodes D1 to Dn by the driver 21 in FIG.
The writing discharge of the cell is performed by applying a scanning pulse to 1 to Xn (scanning electrode).

On the other hand, a value indicating the luminance level of the 8-bit image data a read from the frame memory (hereinafter referred to as a level value) is compared with the set value "63" by the pixel level value comparing section 4 to obtain the image data. When the level value of “a” is equal to or smaller than the set value “63”, 6-bit data excluding the upper 2 bits of data is controlled by the pixel level value comparison unit 4.
It is input to the second light emission control unit 3. In this case, the second light emission control unit 3 performs light emission control according to the number of gradations in each of the subfields SF1 to SF6. Then, the control result is transmitted to the driver 23 of the driving unit 2, whereby the driver 23 applies the light emission pulse (sustain pulse) to the row electrodes Y1 to Yn (sustain electrodes) the number of times corresponding to the number of gradations, The discharge of the cell that has been written and discharged by the scan pulse is maintained.

When the level value of the 8-bit image data a read from the frame memory is larger than the set value “63”, the arithmetic unit 5 subtracts the set value “63” from the level value of the image data a. , The level value of the subtraction result (the level value of pixel data a−63) is calculated by the error diffusion processing unit 6.
Is output to The error diffusion processing unit 6 performs an error diffusion process described later and outputs the processing result to the second second light emission control unit 7, and the second light emission control unit 7 controls each subfield S.
Continuous light emission control using F7 to subfield SF12 is performed. Then, the control result is transmitted to the driver 23 of the drive unit 2 in the same manner, so that the driver 23 applies a number of light emission pulses to the row electrodes Y1 to Yn in proportion to the number of gradations, and the writing discharge is already performed by the scanning pulse. The maintained cell discharge is maintained. If the level value of the 8-bit image data a read from the frame memory is larger than the set value “63”, the light emission by the first light emission control unit 3 in addition to the continuous light emission control by the second light emission control unit 7 Control is also performed.

Next, with reference to FIGS. 4 and 5, the gradation display control of the PDP by the present apparatus will be described more specifically. Input the analog video signal corresponding to the cell to be displayed and
When / D conversion is performed to obtain 8-bit image data a, the level value of the image data a can take a value of 0 to 255. Here, when the level value of the image data a is equal to or less than “63”, the number of gradations is previously set to 1, 2, 4,
Subfield S weighted as 8, 16, 32
The gradation display control using F1, SF2, SF3, SF4, SF5, and SF6 is performed by the first light emission control unit 3.

That is, as shown in FIG. 4, when the pixel level value is "1", gradation display control is performed only by the subfield SF1 within one field period. At this time,
Assuming that the light emission pulse is applied once, when the pixel level value is "2", gradation display control is performed only in the subfield SF2 within one field period, and the light emission pulse is applied twice. Is done. When the pixel level value is "3", the gradation display control is performed only in the subfields SF1 and SF2 within one field period.
One application by F1 and two applications by subfield SF2 are applied three times in total. Further, when the pixel level value is "4", gradation display is performed only in the subfield SF3 within one field period, and the light emission pulse is 4
Applied once.

As described above, as the pixel level value increases, subfields having a large number of gradations are sequentially selected, and gradation display control using the selected subfields is performed. Then, when the pixel level value reaches “63”, gradation display control using all the subfields SF1 to SF6 of the first subfield group is performed within one field period. In this case, the number of application of the light emission pulse
As shown in FIG.
2, once by SF3, SF4, SF5, SF6, 2
This is applied 63 times in total, 4, 8, 16, and 32 times.

Here, when the pixel level value exceeds "63",
When it becomes “95”, as shown in FIG. 5, gradation display control by the first light emission control unit 3 using all the subfields SF1 to SF6 of the first subfield group within one field period. Then, light emission control (continuous light emission control of pixels) using the subfield SF7 of the second subfield group by the second light emission control unit 7 is performed. In this case, the number of application of the light emission pulse is 63 times by the gradation display using all the subfields SF1 to SF6 of the first subfield group, and the continuous light emission using the subfield SF7 of the second subfield group. It is applied a total of 95 times, including 32 times by control. When the pixel level value exceeds “95” and becomes “127”, as shown in FIG. 5, in addition to the display control when the pixel level value is “95”, the second light emission control unit 7 Continuous light emission control using subfield SF8 of the second subfield group is performed. In this case, the number of application of the light emission pulse within one field period is 95 times when the pixel level value is “95”, and 32 times by continuous light emission control using the subfield SF8 of the second subfield group is added. It is applied 127 times in total.

When the pixel level value exceeds "127" and becomes "159", as shown in FIG. 5, in addition to the display control when the pixel level value is "127", the second light emission control is performed. The continuous light emission control by the unit 7 using the subfield SF9 of the second subfield group is performed. In this case, the number of times of application of the light emission pulse in one field period is added 127 times when the pixel level value is “127”, and 32 times by continuous light emission control using the subfield SF9 of the second subfield group. 159 times.

As described above, each time the pixel level value exceeds “63” and subsequently increases by “32”, the same gradation number “32” is obtained.
Are selected so that the subfields SF7 to SF12 having the pixel level values are sequentially added, and the pixel level value is “25” which is the maximum.
5 ", the gradation display control using the first light emission control unit 3 using all the subfields SF1 to SF6 of the first subfield group and the second light emission control unit 7 within one field period. Continuous light emission control is performed using all the subfields SF7 to SF12 of the second subfield group. In this case, the number of application of the light emission pulse is based on all the subfields SF1 to SF6 of the first subfield group. There are a total of 255 times of 63 times by the gradation display control and 6 × 32 times by the continuous light emission control using all the subfields SF7 to SF12 of the second subfield group.

By the way, the level value of the input pixel data a is, for example, between the value "63" and the value "95". Therefore, the value obtained by subtracting the value "63" from the pixel level value is less than the value "32". In this case, error diffusion processing is performed by the error diffusion processing unit 6 in FIG.
It is determined whether or not to perform the continuous light emission control using the subfield SF7 of the subfield group. Further, the level value of the pixel data a is between the value “95” and the value “127”,
Therefore, the value obtained by subtracting the value “63” from the pixel level value and further subtracting the value “1 × 32” from the value is the value “32”.
When the value is less than the above, in addition to the continuous light emission control using the subfield SF7 of the second subfield group, the continuous light emission control using the subfield SF8 of the second subfield group is performed by the above-described error diffusion processing. Is determined.

The level value of the pixel data a is "12".
7 "and the value" 159 ", so the value" 63 "is subtracted from the pixel level value, and the value" 2 "
If the value obtained by subtracting “× 32” is less than the value “32”, the subfields SF7 and SF8 of the second subfield group are used.
In addition to the continuous light emission control using the subfield SF9, it is determined whether or not the continuous light emission control using the subfield SF9 of the second subfield group is performed by the above-described error diffusion processing. Further, the level value of the pixel data a is between the value “159” and the value “191”. Therefore, the value obtained by subtracting the value “63” from the pixel level value and further subtracting the value “3 × 32” from the value is If the value is less than “32”, in addition to the continuous emission control using the subfields SF7 to SF9 of the second subfield group, the subfield SF10 of the second subfield group is used by the above-described error diffusion processing. It is determined whether or not to perform the continuous light emission control.

Further, the level value of the pixel data a is "1".
91 "and the value" 223 ", and thus the value obtained by subtracting the value" 63 "from the pixel level value and further subtracting the value" 4x32 "from the value is less than the value" 32 ". Subfield SF7 of subfield group 2
In addition to the continuous emission control using SF10, the sub-field S of the second sub-field group by the above-described error diffusion processing.
It is determined whether or not to perform continuous light emission control using F11.
Furthermore, the level value of the pixel data a is between the value “223” and the value “255”. Therefore, the value “63” is subtracted from the pixel level value, and the value “5 × 3” is obtained from the value.
When the value obtained by subtracting “2” is less than the value “32”, in addition to the continuous light emission control using the subfields SF7 to SF11 of the second subfield group, the second subfield is generated by the above-described error diffusion processing. It is determined whether or not to perform continuous light emission control using the group subfield SF12.

The relationship between the level value of the input pixel data and the subfield SF used for continuous light emission control in the second subfield group can be expressed by the following equation (1). That is, the pixel level value L can be expressed as L = ΣSFk + a (1). Here, SFk is k counted from subfield SF7 in the second subfield group.
Is the light emission specific gravity of the subfield, and a is 1 ≦ a ≦
SFk.

FIG. 6 is a diagram showing an example of the error diffusion processing by the error diffusion processing section 6. In FIG. 6, P1 is a target pixel which is a target pixel of the error diffusion process, and the error diffusion processing unit 6 calculates an error value E by equation (2) when obtaining an error value of the target pixel P1 by error diffusion. That is, E = ERR (-1, -1) × 1/16 + ERR (0, -1) × 5/16 + ERR (1, -1) × 3/16 + ERR (-1,0) × 7/16 + a × 1 / SFk (2) where ERR (-1, -1), ERR (0, -1), ERR (1, -1) and ERR (-
1, 0) is the pixel P in FIG. 6 adjacent to the pixel of interest P1.
2, P3, P4, and P5 are error values calculated in advance.

When the error value E obtained by the equation (2) is 1 or more, continuous light emission is performed in all the subfields from the subfield SF7 to the (k + 1) th subfield in the second subfield group. Control to be performed. When the error value E obtained by the equation (2) is less than 1, continuous light emission is performed in all the subfields from the subfield SF7 to the kth subfield in the second subfield group. Control.

Here, each of the subfields SF1 to SF1
As described above, the emission specific gravity (number of gradations) of
1,2,4,8,16,32,32,32,32,3
2, 32, and 32, and when the level value of the pixel data a input as the data of the target pixel P1 is, for example, “210”, the first light emission control unit 3 controls all the subfields of the first subfield group. The gradation display control using SF1 to SF6 is performed, and the arithmetic unit 5 subtracts the value “63” from the pixel level value “210” to obtain the value “14”.
7 ”is output to the error diffusion processing unit 6.

In the error diffusion processing section 6, the level value "137" is set.
Is input, the above-described equation (1) is expanded as in equation (3). That is, 147 = SF7 (= 32) + SF8 (= 32) + SF9 (= 32) + SF10 (= 32) + a (= 19) (3) Thereby, continuous light emission is performed in the subfields SF7 to SF10. Control is performed, and the next subfield SF11
Is determined based on the error value E of the pixel of interest P1 calculated by the above equation (2).

Here, when the error value of the adjacent pixels P2 to P5 is 0.5, the equation (2) is as follows: E = 0.5 × (1/16 + 5/16 + 3/16 + 7/16) + 19/32 = 1.099375 (4) In this case, since the error value E of the target pixel P1 is larger than 1, the second light emission control unit 7 is controlled to continuously emit light in the subfields SF7 to SF11, and the error value is obtained. 0.09375 (1.09375-1) is diffused to adjacent pixels P2 to P5.

Further, the error value of the adjacent pixels P2 to P5 is 0.
In the case of 1, equation (2) becomes: E = 0.1 × (1/16 + 5/16 + 3/16 + 7/16) + 19/32 = 0.69375 (5) In this case, the error value E of the target pixel P1 is obtained. Is smaller than 1, the second light emission control unit 7 is controlled to emit light continuously in the subfields SF7 to SF10, and the error value 0.693750 is diffused to the adjacent pixels P2 to P5.

In the present embodiment, the display period of one field is divided into a first sub-field group for performing gradation display and a second sub-field group for performing continuous light emission. In addition, each subfield of the first subfield group is weighted with 1: 2: 4: 8: 16: 32 as each of the six subfields SF1 to SF6, and the second subfield group is composed of six subfields. The light-emitting specific gravity is fixed at 32 for each of the sub-fields SF7 to SF12, but this is merely an example, and the number of sub-fields in the first sub-field group is changed so that, for example, five sub-fields SF1 to SF5 are used. It may be configured and the weighting may be changed. Further, the specific gravity of light emission of each subfield of the second subfield group may be set to be different. Further, the number of each subfield of the first subfield group may not be fixed, but may be varied according to the average luminance level (APL) of the video signal.

[0032]

As described above, according to the present invention, there are provided a plurality of row electrodes arranged for each scanning line and a plurality of column electrodes arranged so as to cross the row electrodes. In an apparatus for displaying a PDP in which one pixel is formed at an intersection of electrodes, one field period of the PDP has a scanning period and a light emitting period, and the light emitting periods are respectively weighted and used for gray scale display of pixels. A first subfield group consisting of M subfields and a second subfield group consisting of N subfields, each of which has a light emission period and is used for continuous light emission of pixels, are input and input. Determining means for determining the magnitude of the luminance level value of the obtained pixel data and a preset value, and selecting a subfield group according to the determination result of the determining means to generate a pixel. In the low-brightness part where the brightness level of the pixel data is low, the first subfield group is selected and gradation display is performed. On the other hand, when the brightness level of the pixel data is high, the first and second subfields are selected. Since it is possible to perform continuous emission display together with gradation display by selecting the subfield group 2, it is possible to suppress the generation of false contours of moving images without impairing gradation deterioration in low-luminance portions in a PDP. it can.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a configuration of a plasma display device according to the present invention.

FIG. 2 shows P constituting the plasma display device.
FIG. 3 is a diagram illustrating a detailed configuration of a DP and a driving unit.

FIG. 3 is a diagram showing an arrangement configuration of subfields in the plasma display device.

FIG. 4 is a diagram showing a display control example of the plasma display device.

FIG. 5 is a diagram showing a display control example of the plasma display device.

FIG. 6 is a diagram illustrating an example of an error dispersion process in the plasma display device.

FIG. 7 is a diagram showing an arrangement configuration of a general subfield.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... PDP, 2 ... drive part, 3 ... 1st light emission control part, 4 ...
Pixel level value magnitude comparing unit, 5 arithmetic unit, 6 error diffusion processing unit, 7 second light emission control unit, 21 to 23 driver
SF1 to SF12: subfield, P1: target pixel,
P2 to P5 ... adjacent pixels.

Claims (3)

[Claims] 1. A pixel having a plurality of row electrodes arranged for each scanning line and a plurality of column electrodes arranged so as to cross the row electrodes, wherein one pixel is formed at an intersection of the row electrodes and the column electrodes. In the plasma display device for performing display of the plasma display panel, one field period of the plasma display panel has a scanning period and a light emitting period, and the light emitting periods are respectively weighted and used for gradation display of the pixels. And a second subfield group consisting of a plurality of subfields each of which has a light emission period and is used for continuous light emission of the pixel. Judging means for judging the magnitude of the brightness level value of the obtained pixel data and a preset setting value; A plasma display device comprising: light emission control means for controlling the light emission of the pixel by selecting a subfield group according to a fixed result. 2. The apparatus according to claim 1, further comprising: subtraction means for subtracting the set value from the brightness level value of the pixel data, wherein the light emission control means determines by the determination means that the brightness level value of the pixel data is small. Then, a sub-field of a light emission period according to the luminance level value is selected from the sub-fields of the first sub-field group to perform gradation display of the pixel, and the pixel data is determined by the determination unit. Is determined to be large, all the subfields in the first subfield group are selected to perform the gradation display of the pixels, and the second
A subfield of a light emission period corresponding to a luminance level value indicating a subtraction result of the subtraction means is selected from the subfield group of the subfields, and the pixel is made to continuously emit light. 3. The apparatus according to claim 2, further comprising: an error diffusion processing unit that performs an error diffusion process when a luminance level value indicating a result of the subtraction by the subtraction unit is input; A plasma display apparatus, wherein a subfield according to the processing result of the error diffusion processing means is selected from among them, and the pixels emit light continuously.